Crosslinked polymers

ABSTRACT

The invention relates to a novel process for the production of mouldings, in particular contact lenses, in which a soluble prepolymer comprising units containing a crosslinkable group and at least one unit containing a modifier is crosslinked in solution, and to mouldings, in particular contact lenses, obtainable by this process. The present invention likewise relates to novel prepolymers which can be employed in the novel process, in particular derivatives of a polyvinyl alcohol having a molecular weight of at least about 2000 which comprises from about 0.5 to about 80%, based on the number of hydroxyl groups in the polyvinyl alcohol, of units of the formulae I and II, II and III or I, II and III, as disclosed in detail in the description, and to crosslinked polymers, either homopolymers or copolymers, made from these novel prepolymers, a process for the preparation of the novel prepolymers and the homopolymers and copolymers obtainable therefrom, to mouldings made from said homopolymers or copolymers, in particular contact lenses made from these homopolymers or copolymers, and to a process for the production of contact lenses using said homopolymers ox copolymers.

This is a divisional of application Ser. No. 08/875,535, filed Jul. 30,1997 U.S. Pat. No. 5,932,674.

The invention relates to a novel process for the production ofmouldings, in particular contact lenses, in which a prepolymercomprising units containing a crosslinkable group and at least one unitcontaining a modifier is crosslinked in solution, and to mouldings, inparticular contact lenses, which are obtainable by this process.

The present invention also relates to novel prepolymers which can beemployed in this crosslinking process, in particular those based onstarting polymers containing functional groups, for example hydroxylgroups, on the polymer chain or functional groups, for example iminogroups, in the polymer chain or functional groups bonded to the polymerskeleton via a bridge, where these functional groups allow covalentbonds to compounds containing a crosslinkable modifier group or anothermodifier group. These starting polymers are, in particular, polyhydroxylcompounds having a 1,2- and/or 1,3-diol structure, such as polyvinylalcohol, or hydrolysed copolymers of vinyl acetate, for examplecopolymers with vinyl chloride, N-vinylpyrrolidone, etc. The inventionfurthermore relates to crosslinked polymers, either homopolymers orcopolymers, made from these novel prepolymers, to a process for thepreparation of the novel prepolymers and the homopolymers and copolymersobtainable therefrom, to mouldings made from said homopolymers orcopolymers, in particular contact lenses made from these homopolymers orcopolymers, and to a process for the production of contact lenses usingthe said homopolymers or copolymers.

The starting polymers are, in particular, derivatives of polyvinylalcohol or copolymers of vinyl alcohol which contain, for example, a1,3-diol skeleton. The crosslinkable group or the further modifier canbe bonded to the starting polymer skeleton in various ways, for examplethrough a certain percentage of the 1,3-diol units being modified togive a 1,3-dioxane which contains a crosslinkable radical or a furthermodifier in the 2-position.

Another possibility is for a certain percentage of hydroxyl groups inthe starting polymer to be esterified by means of an unsaturated organicacid, these ester-bonded radicals containing a crosslinkable group.

In the case of a radical which has been modified to give a 1,3-dioxane,the novel prepolymer is preferably a derivative of polyvinyl alcoholwhich has a mean molecular weight of at least about 2000 and comprisesunits which contain a crosslinkable group and a further modifier. Thefurther modifier serves, inter alia, for weighting, which improves themechanical properties of die moulding, and can contain, for example, anacid or base functionality.

Units containing a crosslinkable group conform, in particular, to theformula I

in which

R is a bivalent radical of a C₁-C₁₂alkane,

R₁ is hydrogen, a C₁-C₆alkyl radical or a cycloalkyl radical,

R₂ is hydrogen or a C₁-C₆alkyl radical,

group if n=0, or the

bridge if n=1,

R₄ is hydrogen or C₁-C₄alkyl,

n is zero or 1, preferably 0, and

R₁₆ and R₁₇, independently of one another, are hydrogen, C₁-C₈alkyl,aryl or cyclohexyl.

Units containing a further modifier conform, in particular, to theformula II

in which

R₁ is hydrogen, a C₁-C₆alkyl radical or a cycloalkyl radical,

R₅ is a monovalent or bivalent radical of a C₁-C₈alkane or a monovalentor bivalent radical of a C₂-C₈olefin,

R₆ is a group of the formula —(—NH—CO—R₇)_(o)(R₈)_(p) or —N(R₉)₂,

R₇ is an unsubstituted or substituted monovalent or bivalent radical ofa C₁-C₈alkane,

R₈ is a heterocyclic group,

R₉ is hydrogen or a C₁-C₆alkyl radical,

n is zero or 1, and

o and p, independently of one another, are zero or 1.

R in the formula I as a bivalent radical of a C₁-C₁₂alkane is a linearor branched radical, in particular a radical of methane, ethane, n- orisopropane, n-, sec- or tert-butane, n- or isopentane, hexane, heptaneor octane. Preferred radicals contain one to four carbon atoms, inparticular one carbon atom.

R₁ and R₂ in the formula I and R₁ and R₉ in the formula II as aC₁-C₆alkyl radical are, for example, a methyl, ethyl, propyl or butylradical. R₁ and R₂ are preferably each hydrogen.

R₄ in the formula I as a C₁-C₄alkyl radical is, for example, an n-butyl,n- or isopropyl or ethyl radical, in particular a methyl radical.

R₅ in the formula II as a radical of a C₂-C₈olefin is a linear orbranched radical, for example a radical of propene, 1-butene, 2-butene,methylpropene, 4-ethyl-2-hexene or 2-methylpentene.

R₅ in the formula II as a radical of a C₁-C₈alkane is a linear orbranched radical, for example a radical of methane, ethane, n- orisopropane, n-, sec- or tert-butane, n- or isopentane, hexane, heptaneor octane.

R₇ in the formula II as a monovalent or bivalent radical of aC₁-C₈alkane is a linear or branched radical, for example a radical ofmethane, ethane, n- or isopropane, n-, sec- or tert-butane, n- orisohexane, heptane or octane.

R₈ in the formula II as a heterocyclic group is, in particular, aradical of a five-membered heterocyclic ring containing one ring memberother than carbon, such as —S—, —O— or —NH—, for example furan,thiophene, pyrrole, pyrrolidone, pyroglutamic acid, maleimides of theformula

(in which R₁₀ and R₁₁, independently of one another, are hydrogen,C₁-C₄alkyl, in particular methyl, or aryl, such as phenyl, or halogen,such as F, Cl or Br, preferably hydrogen or methyl), coumarone,thiocoumarone or indole; a five-membered heterocylic ring containing tworing members other than carbon, such as —O—, —S— or —NH—, for exampleoxazole, isoxazole, thiazole, imidazole, hydantoin of the formula

(in which R₁₂, R₁₃ and R₁₄, independently of one another, are hydrogenor a C₁-C₆alkyl group which is unsubstituted or monosubstituted orpolysubstituted by, for example, COOH or COO(C₁-C₄alkyl)) or pyrazole; afive-membered heterocyclic ring containing three or more ring membersother than carbon, such as —O— or —NH—, for example furazan,1,2,3-triazole, 1,2,4-triazole, 1,3,4-triazole or tetrazole; asix-membered heterocyclic ring containing one ring member other thancarbon, for example —O—, —S— or —NH—, for example pyran, thiopyran,pyridine or quinoline; or a six-membered heterocyclic ring containingmore than one ring member other than carbon, such as —N—, for examplediazines, such as oiazine, miazine, dihydrouracil of the formula

(in which R₁₄ is as defined above) or piazine, vicinal, asymmetrical orsymmetrical triazine or 1,2,3,4-triazine, 1,2,3,5-triazine or1,2,4,5-triazine.

Preferred heterocyclic groups are radicals of five-membered heterocyclicrings containing one ring member other than carbon, in particular —NH—,in particular those of maleimide and pyrrolidone.

R₁₆ and R₁₇ in the formula I as a C₁-C₈alkyl group are a linear orbranched group, for example one of the following: octyl, hexyl, pentyl,butyl, propyl, ethyl, methyl, 2-propyl, 2-butyl or 3-pentyl. R₁₆ ispreferably hydrogen or the CH₃ group, and R₁₇ is preferably a C₁-C₄alkylgroup.

R₁₆ and R₁₇ as aryl are preferably phenyl.

All these groups can be monosubstituted or polysubstituted, examples ofsuitable substituents being the following: C₁-C₄alkyl, such as methyl,ethyl or propyl, —COOH, —OH, —SH, C₁-C₄alkoxy (such as methoxy, ethoxy,propoxy, butoxy or isobutoxy), —NO₂, —NH₂, —NH(C₁-C₄alkyl), —NH—CO—NH₂,—N(C₁-C₄alkyl)₂, phenyl (unsubstituted or substituted by, for example,—OH or halogen, such as Cl, Br or especially I), —S(C₁-C₄alkyl), a 5- or6-membered heterocyclic ring, such as, in particular, indole orimidazole, —NH—C(NH)—NH₂, phenoxyphenyl (unsubstituted or substitutedby, for example, —OH or halogen, such as Cl, Br or especially I), anolefinic group, such as methylene or vinyl, and CO—NH—C(NH)—NH₂.

Preferred substituents are lower alkyl, which here, as elsewhere in thisdescription, is preferably C₁-C₄alkyl, C₁-C₄alkoxy, COOH, SH, —NH₂,—NH(C₁-C₄alkyl), —N(C₁-C₄alkyl)₂ or halogen. Particular preference isgiven to C₁-C₄alkyl, C₁-C₄alkoxy, COOH and SH.

For the purposes of this invention, cycloalkyl is, in particular,cycloalkyl, and aryl is, in particular, phenyl, unsubstituted orsubstituted as described above.

If the radical involved is bonded via an ester group and contains acrosslinkable group, the novel prepolymer is preferably a derivative ofa polyvinyl alcohol having a mean molecular weight of at least about2000 which comprises units of the formula III

in which R₁₅ is hydrogen or a C₁-C₄alkyl group, in particular CH₃, and pis from zero to 6, preferably zero.

Contact lenses based on polyvinyl alcohol have already been disclosedFor example, EP 216 074 discloses contact lenses comprising polyvinylalcohol containing (meth)acryloyl groups bonded via urethane groups. EP189 375 describes contact lenses comprising polyvinyl alcoholcrosslinked by means of polyepoxides.

Furthermore, some specific acetals containing crosslinkable groups havealso already been disclosed. In this connection, we refer, for example,to EP 201 693, EP 215 245 and EP 211 432. EP 201 693 describes, interalia, acetals of unbranched aldehydes having 2 to 11 carbon atomscarrying a terminal amino group which is substituted by aC₃-C₂₄olefinically unsaturated organic radical. This organic radicalcontains a functionality which withdraws electrons from the nitrogenatom, and furthermore the olefinically unsaturated functionality ispolymerizable. EP 201 693 also claims products of the reaction of theacetals characterized above with a 1,2-diol, a 1,3-diol, a polyvinylalcohol or a cellulose. However, such products are not describeddirectly.

If one of the acetals of EP 201 693 is mentioned at all in connectionwith, for example, polyvinyl alcohol, as is the case, inter alia, inExample 17 of that patent application, the acetal which can bepolymerized via its olefinic group is first copolymerized with, forexample, vinyl acetate. The resultant copolymer is then reacted withpolyvinyl alcohol, and an emulsion having a solids content of 37%, a pHof 5.43 and a viscosity of 11,640 cps is obtained. However, none ofthese references describes a combination of a crosslinkable group and anadditional modifier, especially on a polyvinyl alcohol, polyvinylacetate or a copolymer of vinyl acetate and vinylpyrrolidone.

The novel prepolymers have, in particular, a mean molecular weight of atleast about 2000 and comprise from about 0.5 to about 80%, in particularfrom about 1 to 50%, further preferably from about 1 to 25%, preferablyfrom about 2 to 15%, particularly preferably from about 2 to 10%, basedon the number of functional groups, for example hydroxyl groups of thepolyvinyl alcohol, are units of the formula I, II and/or III. The novelprepolymers intended for the production of contact lenses comprise, inparticular, from about 0.5 to about 25%, in particular from about 1 to15%, particularly preferably from about 2 to 12%, based on the number offunctional groups, for example hydroxyl groups of the polyvinyl alcohol,of units of the formula I, II and/or III.

The starting polymers preferably have a mean molecular weight of atleast 2000. The upper limit to their mean molecular weight is up to1,000,000. They preferably have a mean molecular weight of up to300,000, in particular of up to 100,000, very particularly preferably ofup to about 50,000.

Starting polymers which are suitable for the purposes of the invention,in particular polyvinyl alcohols, usually have principally a 1,3-diolstructure. However, they can also contain hydroxyl groups in the form of1,2-glycols, such as copolymer units of 1,2-dihydroxyethylene, as can beobtained, for example, by alkaline hydrolysis of vinyl acetate-vinylenecarbonate copolymers.

In addition, the starting polymers derivatized in accordance with theinvention, in particular polyvinyl alcohols, can also contain smallproportions, for example of up to 20%, preferably of up to 5%, ofcopolymer units of ethylene, propylene, acrylamide, methacrylamide,dimethacrylamide, hydroxyethyl methacrylate, methyl methacrylate, methylacrylate, ethyl acrylate, vinylpyrrolidone, hydroxyethyl acrylate, allylalcohol, styrene or similar comonomers usually used.

Polyvinyl alcohols (PVA) which can be used as starting polymers arecommercially available polyvinyl alcohols, for example Vinol® 107 fromAir Products (MW=22,000 to 31,000, 98-98.8% hydrolysed), Polysciences4397 (MW=25,000, 98.5% hydrolysed), BF 14 from Chan Chun, Elvanol® 90-50from DuPont and UF-120 from Unitika. Other producers are, for example,Nippon Gohsei (Gohsenol®), Monsanto (Gelvatol®), Wacker (Polyviol®) orthe Japanese producers Kuraray, Denki and Shin-Etsu. However, it isadvantageous to use Mowiol® products from Hoechst, in particular thoseof the 3-83, 4-88, 4-98, 6-88, 6-98, 8-88, 8-98, 10-98, 20-98, 26-88 and40-88 type.

The PVAs are prepared by basic or acidic, partial or virtually completehydrolysis of polyvinyl acetate.

As mentioned above, it is also possible to use copolymers of hydrolysedor partially hydrolysed vinyl acetate, which are obtainable, forexample, as hydrolysed ethylene-vinyl acetate (EVA), or vinylchloride-vinyl acetate, N-vinylpyrrolidone-vinyl acetate and maleicanhydride-vinyl acetate.

If the starting polymers are, for example, copolymers of vinyl acetateand vinylpyrrolidone, it is again possible to use commercially availablecopolymers, for example the commercial products available under the nameLuviskol® from BASF.

Particular examples are Luviskol VA 37 HM, Luviskol VA 37 E and LuviskolVA 28.

If the starting polymers are polyvinyl acetates, Mowilith 30 fromHoechst is particularly suitable.

Polyvinyl alcohol is usually prepared by hydrolysis of the correspondinghomopolymeric polyvinyl acetate. In a preferred embodiment, thepolyvinyl alcohol derivatized in accordance with the invention comprisesless than 50% of polyvinyl acetate units, in particular less than 20% ofpolyvinyl acetate units. Preferred amounts of residual acetate units inthe polyvinyl alcohol derivatized in accordance with the invention are,based on the total amount of vinyl alcohol units and acetate units, fromabout 2 to 20%, preferably from about 2 to 16%, in particular from 2 to12%, especially from 0.5 to 3%.

The molecular weights are determined by gel permeation chromatography(GPC) [size exclusion chromatography—SEC] using DMF as solvent and arerelative, unless stated otherwise, to polymethyl methacrylate (PMMA) ascalibration standard.

A polyvinyl alcohol comprising units of the formula I and/or II can beprepared in a manner known per se. For example, a polyvinyl alcoholhaving a mean molecular weight of at least about 2000 which comprisesunits of the formula IV

—CH(OH)—CH₂—

can be reacted with from about 0.5 to 80%, based on the number ofhydroxyl groups in the compound of the formula IV, of a compound of theformula V

and a compound of the formula VI

in which R′ and R″, independently of one another, are hydrogen, loweralkyl or lower alkanoyl, such as acetyl or propionyl, and the othersymbols are as defined under the formulae I and II, in a one-potprocess, in particular in an acidic medium.

The acetals and ketals can also be replaced by the correspondingaldehydes and ketones.

A polyvinyl alcohol comprising units of the formula III can likewise beobtained in a manner known per se by reacting, for example, a polyvinylalcohol having a mean molecular weight of at least about 2000 whichcomprises units of the formula IV

—CH(OH)—CH₂  (IV)

with from about 0.5 to 80%, based on the number of hydroxyl groups, of acompound of the formula VII

in which the symbols R₁₅ and p are as defined under the formula III, inparticular in an acidic medium.

Some compounds analogous to compounds of the formulae V, VI and VII areknown, and these can therefore be prepared in a manner known per se.

For example, the compounds of the formula V where n=zero are obtained,by reacting a compound of the formula VIII

in which the symbols are as defined under the formula V, with a compoundof the formula IX

Hal—CO—R₃  (IX)

in an alkaline medium in the presence of a free-radical inhibitor. Halin the formula IX is halogen, in particular P, Cl or Br, especially Cl.

Examples of compounds of the formula VIII are aminoacetaldehyde dimethylacetal and ω-aminobutyraldehyde diethyl acetal.

Examples of compounds of the formula IX are acryloyl chloride andmethacryloyl chloride.

Compounds of the formula V in which n=1 are prepared, for example, froma compound of the formula VIII by reaction with an azalactone of theformula X

for example 4,4-dimethyl-2-vinyl-4H-oxazol-5-one, where the symbols R₄,R₁₆ and R₁₇ in formula X are as defined under the formula I.

The compounds of the formula VI are, per se, already starting materialsfor the preparation of compounds of the formula II, such asω-aminobutyraldehyde diethyl acetal, crotonaldehyde and butyraldehyde,or can be obtained, for example, by reacting compounds of the formula XI

for example aminoacetaldehyde dimethyl acetal or ω-aminobutyraldehydediethyl acetal, with a compound which introduces the group R₆, such asdimethylmaleic anhydride, dimethylmaleimidylacetyl chloride, aceticanhydride, isobutyryl chloride, succinic anhydride, itaconic anhydride,trimellitic anhydride, sultone or methyl mercaptopropionate or byreacting a compound of the formula V in which n is 0 with, for example,pyrrolidone.

Surprisingly, the prepolymers comprising units of the formulae I, IIand/or III are extremely stable. This is unexpected to the personskilled in the art since higher-functional acrylates, for example,usually require stabilization. If such compounds are not stabilized,rapid polymerization usually occurs. However, spontaneous crosslinkingdue to homopolymerization does not occur with the novel prepolymers. Theprepolymers of the formulae I, II and III can, in addition, be purifiedin a manner known per se, for example by precipitation with acetone,dialysis or ultrafiltration, particular preference being given toultrafiltration. This purification operation allows the prepolymers ofthe formulae I, II and III to be obtained in extremely pure form, forexample as concentrated aqueous solutions, which are free or at leastsubstantially free from reaction products, such as salts, and startingmaterials, or other non-polymeric constituents.

The preferred method for the purification of the novel prepolymers,ultrafiltration, can be carried out in a manner known per se. It ispossible to carry out the ultrafiltration repeatedly, for example fromtwo to ten times. Alternatively, the ultrafiltration can also be carriedout continuously until the desired degree of purity has been achieved.The desired degree of purity can in principle be as great as desired. Asuitable measure of the degree of purity is, for example, the sodiumchloride content of the solution, which can easily be determined in amanner known per se, or GPC.

In addition to the units of the formulae I, II and III, the novelwater-soluble, crosslinkable prepolymers can also comprise furthermodifier units. Of the many possibilities for such modifiers, thefollowing are mentioned by way of example:

Further units containing crosslinkable groups are, for example, those ofthe formulae A and B

in which

R₁ and R₂ embody amino acid radicals and are, independently of oneanother: hydrogen, a

C₁-C₈alkyl group, an aryl group or a cyclohexyl group, these groupsbeing unsubstituted or monosubstituted or polysubstituted,

R₃ is hydrogen or a C₁-C₄alkyl group, and

R₄ is an —O— or —NH— bridge.

Units which contain a bound photoinitiator are, in particular, those ofthe formula C

in which

BR is an —NH—COCH₂_(o) or

bridge or a quaternary salt thereof which has the formula

PI is the radical of a photoinitiator from the class consisting of thebenzoins, such as benzoin ethers, for example benzoin methyl ether,benzoin ethyl ether, benzoin isopropyl ether and benzoin phenyl ether,and benzoin acetate; acetophenones, such as acetophenone,2,2-dimethoxyacetophenone and 1,1-dichloroacetophenone; benzil, benzilketals, such as benzil dimethyl ketal and benzil diethyl ketal;anthraquinones, such as 2-methylanthraquinone, 2-ethylanthraquinone,2-tert-butyl anthraquinone, -chloroanthraquinone and2-amylanthraquinone; furthermore benzophenones, such as benzophenone and4,4′-bis(N,N′-dimethylamino)benzophenone; thioxanthones and xanthones;acridine derivatives, phenazine derivatives; quinoxaline derivatives;and 1-aminophenyl ketones and in particular 1-hydroxyphenyl ketones, inparticular those of the formula

in which

X is —O—, —S— or —N(R₁₂)—,

Y is a counterion, such as H₂SO₄ ^(⊖), F^(⊖), Cl^(⊖), Br^(⊖), I^(⊖),CH₃COO^(⊖), OH^(⊖), BF₄ ^(⊖) or H₂PO₄ ^(⊖),

R₃ is hydrogen, a C₁-C₆alkyl group or a cycloalkyl group,

R₇ is hydrogen; unsubstituted or substituted, linear or branchedC₁-C₁₂alkyl; the

—(CH₂)_(r)—PI group or the —CO—R₁₃ group, in which R₁₃ is linear orbranched C₁-C₆alkyl which is unsubstituted or substituted by —COOH oracrylamide, or an unsubstituted, linear or branched radical of aC₃-C₈olefin,

R₈ is hydrogen, or unsubstituted or substituted, linear or branchedC₁-C₄alkyl so long as

R₇ is not —CO—R₁₃,

R₉ is unsubstituted or substituted, linear or branched C₁-C₆alkyl,unsubstituted or substituted, linear or branched C₁-C₆alkoxy, a6membered carbocyclic or heterocyclic ring, or an unsubstituted linearor branched radical of a C₃-C₈olefin,

R₁₀ is a group of the formula —OR₁₄ or

R₁₁ is unsubstituted or substituted, linear or branched C₁-C₆alkyl, a6-membered carbocyclic or heterocyclic ring, an unsubstituted, linear orbranched radical of a C₃-C₈olefin, or aryl, where

R₉ and R₁₁ together can also be cyclized to form a 5- or 6-memberedcarbocyclic ring,

R₁₂ is hydrogen or unsubstituted, linear or branched C₁-C₄alkyl,

R₁₄ is hydrogen or unsubstituted or substituted, linear or branchedC₁-C₄alkyl,

R₁₅ and R₁₆, independently of one another, are unsubstituted, linear orbranched C₁-C₄alkyl, or R₁₅ and R₁₆ can be bonded together to form a 5-or 6-membered heterocyclic ring,

m is 0 or 1,

n is a number from 1 to 12,

o is a number from 1 to 6, and

r is a number from 2 to 6,

where substituted radicals are substituted, in particular, by C₁-C₄alkylor by C₁-C₄alkoxy, with the following provisos:

if the BR bridge is a quaternary salt, n is a number from 2 to 12;

R₁₄ is not hydrogen if R₉ is a C₁-C₆alkoxy radical; and

R₇ is —CO—R₁₃ when n=1.

Examples of units containing basic groups are those of the formula D

in which R is a linear or branched bivalent radical of a C₁-C₁₂alkane,and R₃ is hydrogen, a C₁-C₆alkyl group or a cycloalkyl group, and R₇ isa basic primary, secondary or tertiary amino group, in particular asecondary or ternary amino group which is substituted by C₁-C₆alkyl, ora quaternary amino group of the formula

—N⊕(R′)₃X⊖

in which R′ is hydrogen or, independently of one another, a C₁-C₁₂alkylradical, in particular a C₁-C₄alkyl radical, and X is a counterion, forexample HSO₄ ^(⊖), F^(⊖), Cl^(⊖), Br^(⊖), I^(⊖), CH₃COO^(⊖), OH^(⊖),BF^(⊖) or H₂PO₄ ^(⊖).

Examples of units containing acidic groups are those of the formula E

in which R and R₃ are as defined under the formula D, and R₈ is theradical of a monobasic, dibasic or tribasic aliphatic or aromatic,saturated or unsaturated organic acid.

Examples of units containing crosslinkable groups bonded via urethane orfurther modifier groups bonded via urethane are those of the formula For G

in which

U is the

or —Y—NH—CO—O—Z—CH═CH₂ group,

X is a bridge having 2 to 12 n atoms, in particular an aliphatic,cycloaliphatic or aromatic bridge, especially alkylene, cyclohexylene orphenylene, which are unsubstituted or in particular substituted by loweralkyl,

R₂ is hydrogen or a C₁-C₄alkyl group,

Y is a bridge having 7 to 12 carbon atoms with the same preferences asfor X,

Z is a C₂- to C₁₂alkylene bridge, which may be interrupted once or morethan once by oxygen atoms, and

A is an organic radical having 1 to 18 carbon atoms, in particular analiphatic, cycloaliphatic or aromatic radical, especially alkyl,cycloalkyl or phenyl, which are unsubstituted or in particularsubstituted by lower alkyl.

Examples of units containing a covalently bonded reactive dye radicalare those of the formula H, I, J or K

in which

RF′ is a radical of the formula

in which

D is the radical of an organic dye,

R₁₄ is a divalent electron-withdrawing group,

U is hydrogen or halogen,

R is the divalent radical of a C₁-C₁₂alkane,

R₁ is hydrogen or C₁-C₄alkyl,

R₃ is hydrogen, C₁-C₆alkyl or cycloalkyl, and

Y is —O— or —N(R₁)—.

The novel prepolymers comprising units of the formula I, II or III and,if desired, one or more of the further modifier units described aboveare water-soluble and uncrosslinked, yet can be crosslinked in anextremely effective and targeted manner, for example byphotocrosslinking, thermal crosslinking or 2+2 photocyclodimerization.

The main crosslinking process used is photocrosslinking in the presenceor absence of an additional vinylic comonomer. The resultant polymersare insoluble in water.

In the case of photocrosslinking, it may be appropriate to add aphotoinitiator which is capable of initiating free-radical crosslinking.The crosslinking can then be initiated by actinic or ionizing radiation.

The photocrosslinking is carried out in a suitable solvent. Suchsolvents are in principle all those which dissolve the prepolymer andany vinylic comonomers additionally used, for example water, alcohols,such as lower alkanols, for example ethanol or methanol, furthermorecarboxamides, such as dimethylformamide or dimethyl sulfoxide, likewisemixtures of suitable solvents, for example mixtures of water with analcohol, for example a water/ethanol or water/methanol mixture.

The photocrosslinking is preferably carried out directly from an aqueoussolution of the novel prepolymers, which can be obtained as a result ofthe preferred purification step, namely ultrafiltration, if desiredafter addition of an additional vinylic comonomer. For example, thephotocrosslinking can be carried out from an approximately 15 to 40%aqueous solution.

The process for the preparation of the novel crosslinked polymerscomprises, for example, photocrosslinking a prepolymer comprising unitsof the formula I, II or III, in particular in essentially pure form, ie.for example, after a single or repeated ultrafiltration, preferably insolution, in particular in aqueous solution, in the presence or absenceof an additional vinylic comonomer.

The vinylic comonomer which can additionally be used in thephotocrosslinking can be hydrophilic, hydrophobic or a mixture ofhydrophobic and hydrophilic vinylic monomers. Suitable vinylic monomersinclude, in particular, those which are usually used in the productionof contact lenses. The term “hydrophilic vinylic monomer” is taken tomean a monomer which, as a homopolymer, typically gives a polymer whichis soluble in water or is capable of absorbing at least 10% by weight ofwater. Analogously, the term “hydrophobic vinylic monomer” is taken tomean a monomer which, as a homopolymer, typically gives a polymer whichis insoluble in water or is capable of absorbing less than 10 percent byweight of water.

In general, from about 0.01 to 80 units of a typical vinylic comonomerreact per unit of formula I, II or III.

If a vinylic comonomer is used, the crosslinked novel polymerspreferably comprise from about 1 to 15 percent, particularly preferablyfrom about 3 to 8 percent, of units of the formulae I, II and/or III,based on the number of functional groups in the starting polymer, forexample hydroxyl groups of the polyvinyl alcohol, which are reacted withfrom about 0.1 to 80 units of the vinylic monomer.

The proportion of vinylic comonomers, if used, is preferably from 0.5 to80 units per unit of the formulae I and II and III, in particular from 1to 30. units of vinylic comonomer per unit of the formulae I and II andIII, particularly preferably from 5 to 20 units per unit of the formulaeI and II and III.

It is furthermore preferred to use a hydrophobic vinylic comonomer or amixture of a hydrophobic vinylic comonomer and a hydrophilic vinyliccomonomer which comprises at least 50 percent by weight of a hydrophobicvinylic comonomer. This allows the mechanical properties of the polymerto be improved without drastically reducing the water content. However,both conventional hydrophobic vinylic comonomers and conventionalhydrophilic vinylic comonomers are in principle suitable for thecopolymerization with polyvinyl alcohol containing groups of the formulaI.

Suitable hydrophobic vinylic comonomers include, without this being acomprehensive list, C₁-C₁₈alkyl acrylates and methacrylates,C₃-C₁₈alkylacrylamides and -methacrylamides, acrylonitrile,methacrylonitrile, vinyl C₁-C₁₈alkanoates, C₂-C₁₈alkenes,C₂-C₁₈haloalkenes, styrene, C₁-C₆alkylstyrene, vinyl alkyl ethers inwhich the alkyl moiety has 1 to 6 carbon atoms, C₂-C₁₀perfluoroalkylacrylates and methacrylates and correspondingly partially fluorinatedacrylates and methacrylates, C₃-C₁₂perfluoroalkylethylthiocarbonylaminoethyl acrylates and -methacrylates, acryloxy- andmethacryloxyalkylsiloxanes, N-vinylcarbazole, C₁-C₁₂alkyl esters ofmaleic acid, fumaric acid, itaconic acid, mesaconic acid and the like.Preference is given to, for example, C₁-C₄alkyl esters of vinylicallyunsaturated carboxylic acids having 3 to 5 carbon atoms or vinyl estersof carboxylic acids having up to 5 carbon atoms.

Examples of suitable hydrophobic vinylic comonomers include methylacrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate,cyclohexyl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, ethylmethacrylate, propyl methacrylate, vinyl acetate, vinyl propionate,vinyl butyrate, vinyl valerate, styrene, chloroprene, vinyl chloride,vinylidene chloride, acrylonitrile, 1-butene, butadiene,methacrylonitrile, vinyltoluene, vinyl ethyl ether,perfluorohexylethylthiocarbonylaminoethyl methacrylate, isobornylmethacrylate, trifluoroethyl methacrylate, hexafluoroisopropylmethacrylate, hexafluorobutyl methacrylate,tris(trimethylsilyloxy)silylpropyl methacrylate,3-methacryloxypropyl-pentarnethyldisiloxane andbis(methacryloxypropyl)tetramethyldisiloxane.

Suitable hydrophilic vinylic comonomers include, without this being acomprehensive list, hydroxy-substituted lower alkyl acrylates andmethacrylates, acrylamide, methacrylamide, lower alkylacrylamides and-methacrylamides, methoxylated acrylates and methacrylates,hydroxy-substituted lower alkylacrylamides and -methacrylamides,hydroxy-substituted lower alkyl vinyl ethers, sodium ethylenesulfonate,sodium styrenesulfonate, 2-acrylamido-2-methylpropanesulfonic acid,N-vinylpyrrole, N-vinylsuccinimide, N-vinylpyrrolidone, 2- and4-vinylpyridine, acrylic acid, methacrylic acid, amino- (where the term“amino” also covers quaternary ammonium), mono(lower alkyl)amino- ordi(lower alkyl)amino(lower alkyl) acrylates and methacrylates allylalcohol and the like. Preference is given to, for example,hydroxy-substituted C₂-C₄alkyl (meth)acrylates, five- to seven-memberedN-vinyllactams, N,N-di-C₁-C₄alkyl(meth)acrylamides and vinylicallyunsaturated carboxylic acids having a total of 3 to 5 carbon atoms.

Examples of suitable hydrophilic vinylic comonomers include hydroxyethylmethacrylate, hydroxyethyl acrylate, acrylamide, methacrylamide,dimethylacrylamide, allyl alcohol vinylpyridine, vinylpyrrolidone,glycerol methacrylate, N-(1,1-dimethyl-3-oxobutyl)acrylamide and thelike.

Preferred hydrophobic vinylic comonomers are methyl methacrylate andvinyl acetate.

Preferred hydrophilic vinylic comonomers are 2-hydroxyethylmethacrylate, N-vinylpyrrolidone and acrylamide.

The novel prepolymers can be converted into mouldings, in particularcontact lenses, in a manner known per so, for example by carrying outthe crosslinking of novel prepolymers in a suitable contact-lens mould.The invention therefore furthermore relates to mouldings essentiallycomprising a novel crosslinked polymer. Further examples of novelmouldings, besides contact lenses, are biomedical mouldings andmouldings for specifically ophthalmic purposes, for example intraocularlenses, eye bandages, mouldings which can be used in surgery, such asheart valves, artificial arteries or the like, furthermore films andmembranes, for example membranes for diffusion control,photostructurable films for information storage, and photoresistmaterials, for example membranes and mouldings for etch resists andscreen printing resists.

A specific embodiment of the invention relates to contact lenses whichcomprise a novel crosslinked polymer made from a prepolymer comprisingunits of the formula I, II or III or essentially comprise or consist ofa novel crosslinked polymer. Contact lenses of this type have a range ofunusual and extremely advantageous properties, including, for example,excellent compatibility with the human cornea, based on a balanced ratiobetween water content (about 50-90% by weight, in particular 60-85% byweight), high oxygen permeability and very good mechanical properties,for example transparency, clarity, freedom from stresses and tearstrength. In addition, the novel contact lenses have high dimensionalstability. Even after autoclaving one or more times at, for example,about 120° C. for about 30-40 minutes, no changes in shape are observed.

It is furthermore emphasized that the novel contact lenses, ie. thosecomprising a crosslinked polymer made from a prepolymer comprising unitsof the formulae I and II, II and III or I, II and III, can be producedvery simply and efficiently compared with the prior art. This is due toa number of factors. Firstly, the starting materials, such as thepolymer backbones, are inexpensive to obtain or prepare. Secondly, it isadvantageous that the prepolymers are surprisingly stable, so that theycan be subjected to very substantial purification. The crosslinking cantherefore be carried out using a prepolymer which requires virtually nosubsequent purification, such as, in particular, complex extraction ofunpolymerized constituents. Furthermore, the crosslinking can be carriedout in purely aqueous solution, so that a subsequent hydration step isunnecessary. Finally, the crosslinking takes place within less than 5minutes, so that the process for the production of the novel contactlenses can be designed to be extremely economical from this point ofview too.

All the above advantages naturally apply not only to contact lenses, butalso to the other mouldings mentioned The totality of the variousadvantageous aspects in the production of novel mouldings results innovel mouldings being particularly suitable as mass-produced articles,for example as contact lenses, which are worn for a short time span(from about 1 to 4 days) and are then replaced by new lenses.

The present invention furthermore relates to the production of the novelmouldings, in particular the novel contact lenses. These processes areillustrated below using the example of contact lenses. However, theseprocesses can also be used for the other mouldings mentioned.

The novel contact lenses can be produced in a manner known per se, forexample in a conventional spin-casting mould, as described, for example,in U.S. Pat. No. 3,408,429, or by the full-mould process in a staticmould, as described, for example, in U.S. Pat. No. 4,347,198.

The present invention also relates to a novel process for the productionof polymeric mouldings, in particular contact lenses, in which awater-soluble prepolymer is crosslinked in solution, and to mouldings,in particular contact lenses, obtainable by this process. The mouldingsobtainable by crosslinking in this way are insoluble, but swellable, inwater.

In detail, this process for the production of mouldings, in particularcontact lenses, comprises the following steps:

a) Preparation of an essentially aqueous solution of a water-solubleprepolymer comprising aa) units containing a crosslinkable group and ab)at least one unit containing a modifier of the formula II

in which

R₁ is hydrogen, a C₁-C₆alkyl radical or a cycloalkyl radical,

R₅ is a monovalent or bivalent radical of the C₁-C₈alkane or amonovalent or bivalent radical of a C₂-C₈olefin,

R₆ is a group of the formula NH—CO—R₇)_(o)(R₈)_(p) or —N(R₉)₂,

R₇ is an unsubstituted or substituted monovalent or bivalent radical ofa C₁-C₈alkane,

R₈ is a heterocyclic group,

R₉ is hydrogen or a C₁-C₆alkyl radical,

n is zero or 1, and

o and p, independently of one another, are zero or 1;

b) introduction of the resultant solution into a mould,

c) initiation of the crosslinking in water or in an organic solvent inwhich the water-soluble, crosslinkable polymer is dissolved, and

d) opening of the mould so that the moulding can be removed.

Unless expressly excluded below, the comments and preferences givenabove in connection with the prepolymers and the comments andpreferences given in connection with the processes for the preparationof polymers and production of mouldings, in particular contact lenses,from these prepolymers also apply in connection with the above-describedprocess comprising steps a), b), c) and d).

The crucial criteria regarding whether a polymer can be employed in thiscrosslinking process are that the prepolymer is soluble in water andcontains crosslinkable groups of the formula I or III.

An essentially aqueous solution of a water-soluble prepolymer can beprepared in a manner known per se, for example by isolating the polymer,for example in pure form, ie. free from undesired constituents, anddissolving the prepolymer in an essentially aqueous medium.

The criterion that the prepolymer is soluble in water is, for thepurposes of the invention, taken to mean in particular that theprepolymer is soluble in an essentially aqueous solution at 20° C. in aconcentration of from about 3 to 90 percent by weight, preferably fromabout 5 to 60 percent by weight, in particular from about 10 to 60percent by weight. If possible in individual cases, prepolymerconcentrations of greater than 90% are also included for the purposes ofthe invention. Particular preference is given to prepolymerconcentrations in solution of from about 15 to about 50 percent byweight, in particular from about 15 to about 40 percent by weight, forexample from about 25 to about 40 percent by weight.

For the purposes of this invention, essentially aqueous solutions of theprepolymer include in particular solutions of he prepolymer in water, inaqueous salt solutions, in particular in aqueous salt solutions havingan osmolarity of from about 200 to 450 milliosmol in 1000 ml (unit:mOsm/l), preferably an osmolarity of from about 250 to 350 mOsm/l, inparticular about 300 mOsm/l, or in mixtures of water or aqueous saltsolutions with physiologically acceptable polar organic solvents, forexample glycerol. Preference is given to solutions of the water-solublecrosslinkable polymers in water alone.

The aqueous salt solutions are advantageously solutions ofphysiologically acceptable salts, such as buffer salts, for examplephosphate salts, which are conventional in the area of contact-lenscare, or isotonicizing agents, in particular alkali metal halides, forexample sodium chloride, which are conventional in the area ofcontact-lens care, or solutions of mixtures thereof. An example of aparticularly suitable salt solution is an artificial, preferablybuffered tear fluid whose pH and osmolarity have been matched to naturaltear fluid, for example an unbuffered, preferably buffered for exampleby phosphate buffer, sodium chloride solution whose osmolarity and pHconform to the osmolarity and pH of human tear fluid.

The above-defined, essentially aqueous solutions of the prepolymer arepreferably pure solutions, ie. those which are free or essentially freefrom undesired constituents. Particular preference is given to solutionsof the prepolymer in pure water or in an artificial tear fluid asdescribed above.

The viscosity of the solution of the prepolymer in the essentiallyaqueous solution is unimportant over broad limits. However, it shouldpreferably be a flowable solution which can be shaped without stresses.

The mean molecular weight of the prepolymer is likewise unimportantwithin broad limits. However, the prepolymer preferably has a molecularweight of from about 10,000 to about 200,000.

The prepolymer used in accordance with the invention must furthermore,as mentioned, contain crosslinkable groups of the formula I or III. Theterm crosslinkable units or groups is taken to mean, in addition to thegroups mentioned, all conventional crosslinkable groups known to theperson skilled in the art. Particularly suitable crosslinkable groupsare. those which contain carbon-carbon double bonds. However, in orderto demonstrate the a variety of crosslinkable groups which are suitable,crosslinking mechanisms which may be mentioned here, merely by way ofexample, are free-radical polymerization, 2+2 cycloaddition, Diels-Alderreaction, ROMP (ring opening metathesis polymerization), vulcanization,cationic crosslinking and epoxy curing.

Suitable polymeric backbones, in addition to the starting polymersmentioned at the outset, are materials as have in some cases alreadybeen proposed as contact-lens materials, for example polymeric diolsother than PVA, polymers comprising saccharides, polymers comprisingvinylpyrrolidone, polymers comprising alkyl (meth)acrylates, polymerscomprising alkyl (meth)acrylates which are substituted by hydrophilicgroups, such as hydroxyl, carboxyl or amino groups, polyalkyleneglycols, or copolymers or mixtures thereof.

The crosslinkable polymer (prepolymer) used in accordance with theinvention comprises the units containing one or more differentcrosslinkable group(s) and, if desired, the units containing the furthermodifier(s), reactive dye radicals and photoinitiator radicals, etc, ina total amount of from about 0.5 to 80%, preferably from 1 to 50%,advantageously from 1 to 25%, in particular from 2 to 15%, particularlypreferably from 2 to 10%, based on the number of functional groups inthe starting polymer, for example hydroxyl groups in the polyvinylalcohol.

Polymers (prepolymers) which can be crosslinked in accordance with theinvention and are intended for the production of contact lensescomprise, in particular, from about 0.5 to about 25%, especially fromabout 1 to 15%, particularly preferably from about 2 to 12%, of theseunits.

As already mentioned, for a prepolymer to be suitable in the novelprocess, it is essential that it is crosslinkable and water-soluble.

Furthermore, the prepolymer is advantageously stable in theuncrosslinked state, so that it can be subjected to purification, asdescribed above in connection with compounds comprising units of theformulae I, II and III. The prepolymers are preferably employed in thenovel process in the form of pure solutions. The prepolymers can beconverted into the form of pure solutions as described below, forexample.

The water-soluble, crosslinkable prepolymers used in the novel processcan preferably be purified in a manner known per se, for example byprecipitation with organic solvents, such as acetone, filtration andwashing, extraction in a suitable solvent, dialysis or ultrafiltration,particular preference being given to ultrafiltration. This purificationoperation allows the crosslinkable polymers to be obtained in extremelypure form, for example as concentrated aqueous solutions, which arereferred to hereinafter as pure or essentially pure. This term isunderstood to refer to a crosslinkable polymer or to a solution thereofwhich is free or at least substantially free from undesiredconstituents.

Undesired constituents in this context are generally all constituentswhich are physiologically undesired, especially monomeric, oligomeric orpolymeric starting compounds used for the preparation of thewater-soluble, crosslinkable polymer, or byproducts formed during thepreparation of the water-soluble, crosslinkable polymer. Preferreddegrees of purity of these constituents are less than 0.01%, inparticular less than 0.001%, very particularly preferably less than0.0001% (1 ppm). It is to be noted, however, that there may be presentin the solution, for example by formation as byproducts during thepreparation of the water-soluble, crosslinkable polymer, constituentswhich are not undesired from a physiological point of view, such as forexample sodium chloride. Preferred degrees of purity of theseconstituents are less than 1%, in particular less than 0.1%, veryparticularly preferably less than 0.01%. In most cases such levels ofconstituents may be obtained by applying 3 to 4 repeated ultrafiltrationcycles.

The preferred process for the purification of the prepolymers used inthe novel process, namely ultrafiltration, can be carried out in amanner known per se. The ultrafiltration can be carried out repeatedly,for example from two to ten times. Alternatively, the ultrafiltrationcan also be carried out continuously until the desired degree of purityhas been achieved. The desired degree of purity can in principle bechosen to be as great as desired.

In a preferred embodiment of the crosslinking process, an essentiallyaqueous solution of the prepolymer which is essentially free fromundesired constituents, for example free from monomeric, oligomeric orpolymeric starting compounds used for the preparation of the prepolymer,and/or free from by-products formed during the preparation of theprepolymer, is prepared in step a) and used further. This essentiallyaqueous solution is particularly preferably a purely aqueous solution ora solution in an artificial tear fluid as described above. It isfurthermore preferred for the crosslinking process to be carried outwithout addition of a comonomer, for example a vinylic comonomer.

Owing to the abovementioned measures and in particular owing to acombination of said measures, the novel process is carried out using asolution of the prepolymer containing no or essentially no undesiredconstituents requiring extraction after crosslinking.

It is therefore a particular feature of this preferred embodiment of thecrosslinking process that extraction of undesired constituents is notnecessary after the crosslinking.

The novel process is therefore preferably carried out in such a way thatthe essentially aqueous solution of the prepolymer is free oressentially free from undesired constituents, in particular frommonomeric, oligomeric or polymeric starting compounds used for thepreparation of the prepolymer, or from by-products formed during thepreparation of the prepolymer, and/or that the solution is used withoutaddition of a comonomer.

An addition which may be added to the solution of the prepolymer is aphotoinitiator for the crosslinking so long as an initiator is necessaryfor crosslinking of the crosslinkable groups. This may be the case, inparticular, if the crosslinking takes place by photocrosslinking.

In the case of photocrosslinking, it is expedient to add an initiatorwhich is capable of initiating free-radical crosslinking and is readilysoluble in water. Examples thereof are known to the person skilled inthe art; suitable photoinitiators which may be mentioned specificallyare benzoins, such as benzoin, benzoin ethers, such as benzoin methylether, benzoin ethyl ether, benzoin isopropyl ether and benzoin phenylether, and benzoin acetate; acetophenones, such as acetophenone,2,2-dimethoxyacetophenone and 1,1-dichloroacetophenone; benzil, benzilketals, such as benzil dimethyl ketal and benzil diethyl ketal,anthraquinones, such as 2-methylanthraquinone, 2-ethylanthraquinone,2-tert-butylanthraquinone, 1-chloroanthraquinone and2-amylanthraquinone; furthermore triphenylphosphine, benzoylphosphineoxides, for example 2,4,6-trimethylbenzoyl-diphenylphosphine oxide,benzophenones, such as benzophenone and4,4′-bis(N,N′-dimethylamino)benzophenone; thioxanthones and xanthones;acridine derivatives; phenazine derivatives; quinoxaline derivatives and1-phenyl-1,2-propanedione 2-O-benzoyl oxime; 1-aminophenyl ketones and1-hydroxyphenyl ketones, such as 1-hydroxycyclohexylphenyl ketone,phenyl 1-hydroxyisopropyl ketone, 4-isopropylphenyl 1-hydroxyisopropylketone, 2-hydroxy-1-[4-(2-hydroxyethoxy)phenyl]-2-methylpropan-1-one,1-phenyl-2-hydroxy-2-methylpropan-1-one, and2,2-dimethoxy-1,2-diphenylethanone, all of which are known compounds.

Particularly suitable photoinitiators, which are usually used incombination with UV lamps as light source, are acetophenones, such as2,2-dialkoxybenzophenones and hydroxyphenyl ketones, for example theinitiators obtainable under the names IRGACURE®2959 and IRGACURE®1173.

Another class of photoinitiators usually employed when argon ion lasersare used are benzil ketals, for example benzil dimethyl ketal.

The photoinitiators are added in effective amounts, expediently inamounts of from about 0.1 to about 2.0% by weight, in particular from0.3 to 0.5% by weight, based on the total amount of the prepolymer.

The resultant solution can be introduced into a mould using methodsknown per se, such as, in particular, conventional metering, for exampledropwise. The novel contact lenses can be produced in a manner known perse, for example in a conventional spin-casting mould, as described, forexample, in U.S. Pat. No. 3,408,429, or by the full-mould process in astatic mould, as described, for example, in U.S. Pat. No. 4,347,198.Appropriate moulds are made, for example, of polypropylene. Examples ofsuitable materials for reusable moulds are quartz and saphire glass.

The prepolymers which are suitable in accordance with the invention canbe crosslinked by irradiation with ionizing or actinic radiation, forexample electron beams, X-rays, UV or VIS light, ie. electromagneticradiation or particle radiation having a wavelength in the range fromabout 280 to 650 nm. Also suitable are He/Cd, argon ion or nitrogen ormetal vapour or NdYAG laser beams with multiplied frequency. It is knownto the person skilled in the art that each selected light sourcerequires selection and, if necessary, sensitization of the suitablephotoinitiator. It has been recognized that in most cases the depth ofpenetration of the radiation into the water-soluble, crosslinkablepolymer and the rate are in direct correlation with the absorptioncoefficient and concentration of the photoinitiator.

However, the crosslinking can also be initiated thermally. It should beemphasized that the crosslinking can take place in a very short time inaccordance with the invention, for example in less than five minutes,preferably. in less than one minute, in particular in up to 30 seconds,particularly preferably as described in the examples.

Apart from water, which is preferred, the crosslinking medium canadditionally be any medium in which the prepolymer is soluble. In thecase of polyvinyl alcohol as the principal polymer backbone, allsolvents which dissolve polyvinyl alcohol are suitable, such asalcohols, for example ethanol, glycols, glycerol, piperazine (atelevated temperature), diamines, such as triethylenediamine, formamide,dimethylformamide, hexamethylphosphoric triamide, dimethyl sulfoxide,pyridine, nitromethane, acetonitrile, nitrobenzene, chlorobenzene,trichloromethane, dioxane and aqueous solutions of tetraalkylammoniumbromide and iodide.

The opening of the mould so that the moulding can be removed can becarried out in a manner known per se. Whereas the process proposed inthe prior art (U.S. Pat. Nos. 3,408,429 and 4,347,198) requiressubsequent purification steps at this point, for example by extraction,and also steps for hydration of the resultant mouldings, in particularcontact lenses, such steps are unnecessary here.

Since the solution of the prepolymer preferably comprises no undesiredlow-molecular-weight constituents, the crosslinked product alsocomprises no such constituents. Subsequent extraction is thereforeunnecessary. Since the crosslinking is carried out in an essentiallyaqueous solution, subsequent hydration is unnecessary. These twoadvantages mean, inter alia, that complex subsequent treatment of theresultant mouldings, in particular contact lenses, is unnecessary. Thecontact lenses obtainable by the crosslinking process are thereforedistinguished, in an advantageous embodiment, by the fact that they aresuitable for their intended use without extraction. The term ‘intendeduse’ in this connection is taken to mean, in particular, that thecontact lenses can be employed in the human eye. The contact lensesobtainable by the crosslinking process are furtherore distinguished inan advantageous embodiment by the fact that they are suitable for theirintended use without hydration.

The novel process therefore proves to be extremely suitable for theefficient production of a large number of mouldings, such as contactlenses, in a short time. The contact lenses obtainable by this processhave, inter alia, the advantages over the contact lenses known from theprior art that they can be used as intended without subsequent treatmentsteps, such as extraction or hydration.

The examples below serve to further illustrate the invention. In theexamples, unless expressly stated otherwise, amounts are by weight andtemperatures are given in degrees celcius. Examples are not intended torepresent any restriction of the invention, for example to the scope ofthe examples.

EXAMPLE 1

220 g (5.5 mol) of sodium hydroxide are dissolved in 300 g of water and700 g of ice in a 3 liter reactor fitted with stirrer and cooling means.The sodium hydroxide solution is cooled to 10° C., and 526 g (5.0 mol)of aminoacetaldehyde dimethyl acetal and 50 mg of4-hydroxy-2,2,6,6-tetramethylpiperidine 1-oxide (free-radical inhibitor)are added. 548.6 g (5.5 mol) of methacryloyl chloride are slowly addedto this solution at 10° C. over the course of 3.5 hours. When theaddition is complete, the pH slowly drops to 7.2, and amine is no longerdetectable by GC. The reaction mixture is extracted with 500 ml ofpetroleum ether in order to remove impurities, and the water phase issaturated with sodium chloride and extracted three times with 500 ml oftert-butyl methyl ether. The organic phase is dried using magnesiumsulfate, filtered and evaporated on a rotary evaporator. The 882.2 g ofyellowish oil obtained are slowly stirred into 2000 ml of petroleumether at −10° C. using an Ultraturax. The product crystallizes, and isfiltered off and dried, giving 713.8 g of methacrylamidoacetaldehydedimethyl acetal (86% of theory), melting point 30-32° C. The product is99.7% pure according to GC.

EXAMPLE 2

40 g (1.0 mol) of sodium hydroxide are dissolved in 100 g of water and200 g of ice in a 1 liter reactor fitted with stirring and coolingmeans. The sodium hydroxide solution is cooled to 10° C., and 105.1 g(1.0 mol) of aminoacetaldehyde dimethyl acetal and 10 mg of theinhibitor 4hydroxy-2,2,6,6-tetramethylpiperidine 1-oxide are added. 995g (1.1 mol) of acryloyl chloride are slowly added to this solution at10° C. over the course of 2 hours. The pH drops slowly and is finallyset to pH=7. Amine is no longer present according to GC. The reactionmixture is saturated with sodium chloride and extracted three times with200 ml of tert-butyl methyl ether. The organic phase is dried, filteredand evaporated on a rotary evaporator. The resultant oil is extractedthree times with petroleum ether and subsequently re-dried on a rotaryevaporator, giving 130 g of acrylamidoacetaldehyde dimethyl acetal (81%of theory) as an oil. The product is 99% pure according to GC.

EXAMPLE 3

N-(4,4-Diethoxybutyl)acrylamide.

The preparation is carried out analogously to the procedure of Example 2from ω-aminobutyraldehyde diethyl acetal and acryloyl chloride. An oilwith a purity of 99.1% according to GC is obtained in a yield of 97%.

NMR data: 1.20 ppm (t) 6 methyl protons, 1.62 ppm (broad) 4 methyleneprotons, 3.21 ppm (dd) 2 methylene protons, 3.49 and 3.68 ppm (m) 4methoxy protons, 4.50 ppm (t)1 acetal proton, 5.9-6.2 ppm 3 vinylprotons, 6.29 ppm 1 amide proton.

EXAMPLE 4

N-(4,4-Diethoxybutyl)-2-methylacrylamide.

The preparation is carried out analogously to the procedure of Example 1from ω-aminobutyraldehyde diethyl acetal and methacryloyl chloride. Anoil having a purity of 94.7% according to GC is obtained in a yield of83%.

NMR data: 1.23 ppm (t) 6 methyl protons, 1.65 ppm (broad) 4 methyleneprotons, 1.95 ppm (s) 3 methyl protons, 3.34 ppm (dd) 2 methyleneprotons, 3.5 and 3.65 ppm (m) 4 methoxy protons, 4.49 ppm (t) acetalproton, 530 and 5.67 ppm (s) 2 vinyl protons, 6.17 ppm NH proton.

EXAMPLE 5

N-[1-(2,2-Dimethoxyethylcarbamoyl)-1-methylethyl]acrylamide.

62.62 g (0.45 mol) of 4,4-dimethyl-2-vinyl-4H-oxazol-5-one (azalactone)are introduced into 275 g of tert-butyl methyl ether. 47.34 g (0.45 mol)of aminoacetaldehyde dimethyl acetal are slowly added with stirring. Theproduct is formed as a white precipitate, which is filtered off, washedwith tert-butyl methyl ether and dried, giving 106 g (96.5% of theory)of a white product of melting point 80-82° C.

Analysis: found calc. C: 54.13% 54.08%  H: 8.49% 8.25% N: 11.42% 11.47%

NMR data: 1.60 ppm (s) 6 methyl protons, 3.39 ppm (s) 6 methoxy protons,3.42 ppm (d) 2 methylene protons, 437 ppm (t) 1-acetal proton, 5.6-6.3ppm (m) 3 vinyl protons, 6.43 and 6.54 ppm 2 NH protons.

EXAMPLE 6

N-[1-(2,2-Diethoxybutylcarbamoyl)-1-methylethyl]acrylamide.

The product was prepared analogously to Example 5 fromω-aminobutyraldehyde diethyl acetal and azalactone. Yield: 81% oftheory. m.p. 60-64° C.

Analysis: found calc. C: 59.83%  59.98% H: 9.36% 9.40% N: 9.26% 9.33%

NMR data: 1.2 ppm (t) 6 methyl protons, 1.61 ppm (s) 6 methyl and 4methylene protons, 3.30 ppm (d) 2 methylene protons, 3.43-3.69 ppm (m) 4methylene protons, 4.49 ppm (t) acetal proton, 5.6-6.3 ppm (m) 3 vinylprotons, 652 and 6.69 ppm 2 NH protons.

EXAMPLE 7

1-(2,2-Dimethoxyethyl)3,4-dimethylpyrrole-2,5-dione.

84 g (0.66 mol) of dimethylmaleic anhydride are dissolved in 150 ml oftoluene, and 70 g (0.66 mol) of aminoacetaldehyde dimethyl acetal areadded. The solution is heated to the boil, and the water formed isseparated off by means of a water separator. When the reaction iscomplete, the solvent is removed by distillation, and the residue isdistilled, giving 127 g (90% of theory) of the product of boiling point160° C. at 0.03 mbar which is a single product according to TLC and GC.NMR data: 2.97 (s) 6- methyl protons, 3.34 ppm (s) 6 methoxy protons,3.61 ppm (d) 2 methyl protons, 4.66 ppm (t) 1 acetal proton.

Analysis: found calc. C: 56.36%  56.33% H: 7.12% 7.09% N: 6.56% 6.57%

EXAMPLE 8

N-[2,2-Dimethoxyethyl]-2-[3,4dimethyl-2,5-dioxo-2,5-dihydro-pyrrol-1-yl)acetamide.

100 g (0.49 mol) of dimethylmaleimidylacetyl chloride are reacted with50.2 g (0.49 mol) of aminoacetaldehyde dimethyl acetal analogously toExample 1. Extraction with methylene chloride gives 127.5 g (95% oftheory) of crude product. Recrystallization from hot water gives 102 g(77% of theory) of product of m.p. 99.4-99.9° C.

Analysis: found calc. C: 53.40% 53.33%  H: 6.81% 6.71% N: 10.36% 10.36%

EXAMPLE 9

N-(4,4-Diethoxybutyl)-3,4dimethylpyrrole-2,5-dione.

23.4 g (0.186 mol) of dimethylmaleic anhydride and 30 g (0.186 mol) ofω-aminobutyraldehyde diethyl acetal are reacted analogously to Example7. Distillation at 106° C. and 0.01 mbar gives 42.2 g (85% of theory) ofcolourless oil.

Analysis: found calc. C: 62.44%  62.43% H: 8.65% 8.61% N: 5.12% 5.20%

EXAMPLE 10

N-[2,2-Dimethoxyethyl]acetamide.

30.6 g (0.3 mol) of acetic anhydride are added to 315 g (0.3 mol) ofaminoacetaldehyd dimethyl acetal in 50 ml of methylene chloride. Whenthe exothermic reaction is complete, the methylene chloride is removedby distillation, the product is distilled, giving 42 g of colourlessproduct (97% of theory), boiling point 110° C., 0.001 mbar. The productis a single compound according to GC

Analysis: found calc. C: 49.14%  48.97% H: 8.90% 8.90% N: 9.70% 9.52%

EXAMPLE 11

N-[2,2-Dimethoxyethyl]isobutyramide.

The product is prepared analogously to Example 1 from isobutyrylchloride and aminoacetaldehyde dimethyl acetal. Distillation at 98° C.and 0.01 mbar gives a yield of 77 %. According to GC; the product has apurity of 98%.

Analysis: found calc. C: 54.98%  54.84% H: 9.78% 9.78% N: 7.94% 7.99%

EXAMPLE 12

N-[2,2-Dimethoxyethyl]succinic Monoamide.

50.4 g (0.5 mol) of freshly distilled succinic anhydride are dispersedin 100 ml of methylene chloride. 52.75 g (0.5 mol) of aminoacetaldehydedimethyl acetal are added, and the mixture is boiled under reflux. After30 minutes, the homogeneous solution is evaporated in vacuo and freedfrom solvent at 60° C. under a high vacuum, giving a viscous oil which,according to titration with sodium hydroxide solution, has a purity of99A %. NMR data: 2.63 ppm (m) 4 methylene protons of succinic acid, 3.42ppm (s) 6 methoxy protons, 4.42 ppm (t) 1 acetal proton, 3.6 ppm (d) 2methylene protons, 6.60 ppm (t) 1 amide proton, 9.79 ppm 1 acid proton

EXAMPLE 13

N-[2,2-Dimethoxyethyl]-3-mercaptopropionamide.

30.8 g (0.25 mol) of methyl mercaptopropionate and 28.7 g (0.27mol) ofaminoacetaldehyde dimethyl acetal are introduced into a 250 mlround-bottom flask fitted with Vigreux column and distillationattachment The mixture is kept at 120° C., and the methanol formed isremoved by distillation. When the methanol formation is complete, theproduct is distilled at 180° C. under a water-pump vacuum, giving 26 g(52% of theory) of a colourless oil.

Analysis: found calc. C: 43.65% 43.50%  H: 7.89% 7.82%  N: 7.89% 7.82%S: 15.29% 16.59%

EXAMPLE 14

N-[2,2-Dimethoxyethyl]-3-[2-oxopyrrolidin-1-yl]propionamide.

10 g (62.8 mmol) of the acrylamido acetal from Example 2 are mixed with6 g (70.5 mmol) of pyrrolidone and, after addition of one drop of TritonB, the mixture is warmed to 80° C. After 10 minutes, the reaction isterminated. The thin-layer chromatogram shows no UV absorbing acetal.The product is subsequently freed from traces of solvent under a highvacuum. It is a single compound according to TLC. NMR data: 2 methyleneprotons at each of 2.0, 2.4, 2.5, 3.3, 3.4 and 3.6 ppm(t), 6 methoxyprotons at 3.35 ppm(s), 1 acetal proton at 4.4 ppm(t), 1 amide proton at7.2 ppm.

Example 15

General Method for the Preparation of High-Acetate Products of theReaction of PVA with Acetals or Aldehydes.

300 g of a PVA (Mowiol 4-88, unless stated otherwise) are introducedinto a 2 liter twin-jacket reactor fitted with stirrer and thermometer,800 g of demineralized water are added, and the mixture is warmed to 95°C. with stirring. After one hour, all the reactants have dissolved togive a clear solution, which is cooled to 20° C. A crosslinkable acetalin the amount given in the examples, if desired together with one ormore acetal(s), 440 g of acetic acid, 100 g of conc. hydrochloric acid(37%) and sufficient demineralized water to give a total of 200 g ofreaction solution are added. The mixture is stirred at 20° C. for 20hours.

Isolation can be carried out by ultrafiltration: the reaction mixture iscooled to 15° C. and the pH is adjusted to 3.6 by means of aqueous NaOH(5%). The polymer solution is filtered through a 0.45 μm filter andpurified by ultrafiltration. The ultrafiltration is carried out using a1KD Omega membrane from Filtron. The ultrafiltration is continued to aresidual sodium chloride content of 0.004%. Before the purification iscompleted, the solution is adjusted to pH=7 using 0.1 N sodium hydroxidesolution. Concentration gives 1995 g of a 1454% polymer solution (92% oftheory); N content (Kjendahl determination)=0.683%, acetate content(determined by hydrolysis)=2.34 meq/g, intrinsic viscosity=0.310, 0.5meq/g of double bonds (determined by microhydrogenation), 15.3 meq/g offree hydroxyl groups (determined by re-acetylation), GPC analysis (inwater): M_(w)=19,101, M_(n)=7522,M_(w)/M_(n)=2.54.

The isolation can also be carried out by precipitation: the reactionmixture is adjusted to pH 3.6 by means of triethylamine and precipitatedin acetone in a ratio of 1:10. The precipitate is separated off,dispersed twice in ethanol and once in acetone and dried. The resultantproduct has the same properties as that obtained above byultrafiltration.

EXAMPLE 16

General Method for the Preparation of Low-Acetate Products of theReaction of PVA with Acetals or Aldehydes.

300 g of a PVA (Mowiol 4-88, unless stated otherwise) are introducedinto a 2 liter twin-jacket reactor fitted with stirrer and thermometer,800 g of demineralized water are added, and the mixture is warmed to 95°C. with stirring. After one hour, all the reactants have dissolved togive a clear solution, which is cooled to 20° C. A crosslinkable acetalin the amount given in the examples, if desired together with one ormore acetal(s), 440 g of acetic acid, 100 g of conc. hydrochloric acid(37%) and sufficient demineralized water to give a total of 2000 g ofreaction solution are added. The mixture is stirred at 20° C. for 20hours. After 20 hours, a sample of the reaction solution is titratedwith NaOH, and the degree of hydrolysis of the PVA determined: HCl=1.034meq/g, acetic acid=0.265 meq/g, corresponding to a residual acetatecontent of 35 mol %. The reaction mixture is stirred at 25° C. for afurther two hours and re-titrated: HCl=1.034 meq/g, acetic acid =0.277meq/g, corresponding to a residual acetate content of 2.93 mol %.

The isolation can also be carried out by ultrafiltration: the reactionmixture is cooled to 15° C. and adjusted to pH 7 using aqueous NaOH(5%). The polymer solution is filtered through a 0.45 μm filter andpurified by ultrafiltration. The ultrafiltration is carried out by meansof a 1KD Omega membrane from Filtron. The ultrafiltration is continuedto a residual sodium chloride content of 0.002%. 1800 g of a 14.02%polymer solution (86% of theory) are obtained; N content (Kjendahldetermination)=0.741%, acetate content (according to titration)=0.605meq/g, corresponding to 2.91 mol %, intrinsic viscosity=0.327, 0.61meq/g of double bonds (determined by microhydrogenation), 18.13 meq/g offree hydroxyl groups (determined by re-acetylation), GPC analysis (inwater): M_(w)=22,007, M_(n)=9743, M_(w)/M_(n)=2.26.

The isolation can also be carried out by precipitation: the reactionmixture is adjusted to pH 3.6 using triethylamine and precipitated inacetone in a ratio of 1:10. The precipitate is separated off, dispersedtwice in ethanol and once in acetone and dried. The resultant product iscomparable to that obtained above by ultrafiltration.

EXAMPLES 17a) TO 17b)

Products of the reaction of PVA (Mowiol 3-83, Hoechst), residual acetatecontent 17 mol %, M_(w)=8261, M_(n)=3646, M_(w)/M_(n)=2.26, intrinsicviscosity (dl/g)=0.278 by preparation method of Example 15, isolation byultrafiltration using a 1KD membrane (Millipore):

17a): 30 g of acetal from Example 2,500 g of added acetic acid,

Prepolymer data (sol):

Intrinsic viscosity: [dl/g]=0.329

N content 0.79%

Acetal content: 0.62 meq/g

Acetate content: 15.3 mol %

M_(w): 18,500, M_(n): 6735, M_(w)/M_(n): 2.74

Solids content:

30% in the sol state result in 30.2% in the gel state.

17b): 30 g of acetal from Example 1, 500 g of added acetic acid,

Prepolymer data (sol):

Intrinsic viscosity: [dl/g]=0.282

N content 0.789%

Acetal content 0.57 meq/g

Acetate content: 2.81 meq/g, corresponding to 15.1 mol %

M_(w): 14,151, M_(n): 5652, M_(w)/M_(n): 2.58

Solids content:

30% in the sol state result in 30.0% in the gel state.

EXAMPLES 17c) TO e)

Products of the reaction of PVA (Mowiol 26-88, Hoechst), residualacetate content 12 mol %, by the preparation method of Example 15,isolation by ultrafiltration using a 5KD membrane (Millipore):

17c): 7.0 g of acetal from Example 2, 560 g of added acetic acid, 140 gof PVA (26-88) used

Prepolymer data (sol):

Intrinsic viscosity: [dl/g]=0.844

N content: 0.36%

Acetal content: 0.255 meq/g

Acetate content: 12.8 mol %

M_(w): 102,341, M_(n): 37,844, M_(w)/M_(n): 2.70

Solids content:

19.6% in the sol state result in 15.2% in the gel state.

17d): 14 g of acetal from Example 2, 560 g of added acetic acid,

140 g of PVA (26-88) used.

Prepolymer data (sol):

Intrinsic viscosity: [dl/g]=0.842

N content: 0.791%

Acetal content: 0.56 meq/g

Acetate content: 13.4 mol %

M_(w): 78,214, M_(n): 31,475, M_(w)/M_(n): 2.48

Solids content:

16.6% in the sol state result in 21.4%

in the gel state.

20.3% in the sol state result in 25.8%

in the gel state.

17e): A 1:1 mixture of 15% solutions from Examples 17c) and 17d) give asolids content (of the dimensionally stable contact lens) of 17.3% inthe gel state resulting from 15% in the sol state. A mixture of thistype is suitable for adjusting the solids content and thus the shrinkageof a moulding.

EXAMPLES 18A) TO D)

Products of the reaction of PVA (Mowiol 4-88, Hoechst) with variousacetal crosslinking agents by the general preparation method of Example15, isolation, purification and concentration carried out byultrafiltration (5KD Millipore membrane):

18a): 37.3 g of acetal from Example 3, 500 g of added acetic acid,

Prepolymer data (sol):

Intrinsic viscosity: 0.363 dl/g

N content: 0.77%

Crosslinking agent content: 055 meq/g

Acetate content: 12.8 mol %

Solids content:

30% in the sol state result in

30.9% in the gel state.

18b): 53.0 g of acetal from Example 4, 500 g of added acetic acid,

Prepolymer data (sol):

Intrinsic viscosity: 0.324 dl/g

N content: 0.73%

Crosslinking agent content: 0.52 meq/g

Acetate content: 12.7 mol %

Solids content:

30% in the sol state result in

29.3% in the gel state.

18c): 56.5 g of acetal from Example 5, 500 g of added acetic acid,

Prepolymer data (sol):

Intrinsic viscosity: 0.330 dl/g

N content: 1.43%

Crosslinking agent content: 0.1 meq/g

Acetate content: 12.7 mol %

Solids content:

30% in the sol state result in

30.0% in the gel state.

18d): 69.36 g of acetal from Example 6, 500 g of added acetic acid,

Prepolymer data (sol):

Intrinsic viscosity: 0345 dl/g

N content: 1.43%

Crosslinking agent content: 0.1 meq/g

Acetate content: 12.9 mol %

Solids content:

30% in the sol state result in

30.15% in the gel state.

18e): 100 g of PVA (Mowiol 488, Hoechst) are dissolved in 334 g ofwater, and 166 g of methacrylic acid, 166 g of acetic acid and 665 g ofconc. hydrochloric acid are added. The reaction mixture is stirred at40° C. for 5 days in contact with air.

Isolation: After addition of 5% sodium hydroxide solution, the pH isadjusted to 3.6 and the polymer is precipitated by means of NaClsolution. The precipitated polymer is subsequently dissolved in waterand purified by ultrafiltration through a 5KD Millipore membrane.

Prepolymer data (sol):

Intrinsic viscosity: 0.343 dl/g

Methacrylate content: 7 mol %

Acetate content: 13 mol %

GPC data: M_(w)=16,550, M_(n)=6631, M_(w)/M_(n)=2.49

Solids content:

30% in the sol state result in

33.7% in the gel state.

18f): 100 g of PVA (Mowiol 4-88, Hoechst) are dissolved in 334 g ofwater, and 166 g of acrylic acid, 166 g of acetic acid and 665 g ofconc. hydrochloric acid are added. The reaction mixture is stirred at40° C. for 5 days in contact with air. Isolation: After addition of 5%sodium hydroxide solution, the pH is adjusted to 3.6 and the polymer isprecipitated by means of NaCl solution. The precipitated polymer issubsequently dissolved in water and purified by ultrafiltration througha 5KD Millipore membrane.

Prepolymer data (sol):

Intrinsic viscosity: 0.596 dl/g

Acrylate content: 9 mol %

Acetate content: 13 mol %

GPC data: M_(w)=22,383, M_(n)=8121, M_(w)/M_(n)=2.75

Solids content:

30% in the sol state result in

35.0% in the gel state.

EXAMPLES 19a) TO c)

Products of the reaction of PVA (Mowiol 488, Hoechst) with acetal fromExample 1 and modifier acetal from Example 11, preparation method ofExample 16, reaction time 12 hours at 20° C., isolation byultrafiltration:

19a): 56 g of acetal from Example 1 and 56 g of modifier acetal fromExample 11, preparation method of Example 16:

Prepolymer data (sol):

N content: 2.26%

Total acetal content: 1.61 meq/g

Acetate content: 65 mol %

Cloud point: 36° C.

Solids content:

30% in the sol state result in

40.1% in the gel state.

19b): 46 g of acetal from Example 1 and 56 g of modifier acetal fromExample 11, preparation method of Example 16:

Prepolymer data (sol):

N content: 2.12%

Total acetal content: 1.52 meq/g

Acetate content: 6.6 mol %

Cloud point: 41° C.

Solids content:

30% in the sol state result in

38.2% in the gel state.

19c): 36 g of acetal from Example 1 and 56 g of modifier acetal fromExample 11, preparation method of Example 16:

Prepolymer data (sol):

N content: 1.97%

Total acetal content: 1.41 meq/g

Acetate content: 6.0 mol %

Cloud point: 47° C.

Solids content:

30% in the sol state result in

33.5% in the gel state.

EXAMPLES 20a) TO d)

Products of the reaction of PVA (Mowiol 4-88 or 4-98, Hoechst),preparation method of Example 16, with acetal from Example 1 andmodifier acetal from Example 10, reaction time 12 hours at 20° C.,isolation by ultrafiltration.

20a): 56 g of acetal from Example 1 and 28 g of modifier acetal fromExample 10, preparation method of Example 16:

Prepolymer data (sol):

N content 1.87%

Crosslinking agent content: 0.97 meq/g

Total acetal content 133 meq/g

Acetate content: 65 mol %

Cloud point: 72° C.

Solids content:

30% in the sol state result in

38.5% in the gel state.

20b): 56 g of acetal from Example 1 and 56 g of modifier acetal fromExample 10, preparation method of Example 16:

Prepolymer data (sol):

N content: 2.61%

Crosslinking agent content: 0.97 meq/g

Total acetal content: 1.87 meq/g

Acetate content: 55 mol %

Cloud point: 61° C.

Solids content:

30% in the sol state result in

36% in the gel state.

20c): 56 g of acetal from Example 1 and 100 g of modifier acetal fromExample 10, preparation method of Example 16:

Prepolymer data (sol):

N content: 3.11%

Crosslinking agent content: 1.1 meq/g

Total acetal content. 2.23 meq/g

Acetate content: 7.1 mol %

Cloud point: 46° C.

Solids content:

30% in the sol state result in

37.0% in the gel state.

20d): 26 g of acetal from Example 1 and 96 g of modifier acetal fromExample 10, preparation method of Example 16 using PVA (Mowiol 4-98,Hoechst):

Prepolymer data (sol):

N content 2A8%

Crosslinking agent content: 0.34 meq/g

Total acetal content: 1.78 meq/g

Acetate content: 0.8 mol %

Intrinsic viscosity: 0345 [dl/g]

Solids content:

30% in the sol state result in

28.1% in the gel state.

EXAMPLES 21a) TO d)

Products of the reaction of PVA (Mowiol 4-88, Hoechst), preparationmethod of Example 16 with acetal from Example 1 and the acidic modifieracetal from Example 12, reaction time 12 hours at 20° C., isolation byultrafiltration (3KD membrane):

21 a): 56 g of acetal from Example 1 and 24 g of acidic modifier acetalfrom Example 12, preparation method of Example 16:

Prepolymer data (sol):

N content: 1.66%

Crosslinking agent content: 0.96 meq/g

Total acetal content: 1.19 meq/g

Acetate content: 7.2 mol %

Solids content:

30% in the sol state result in

32.7% in the gel state.

21b): 39 g of acetal from Example 1 and 25 g of acidic modifier acetalfrom Example 12, preparation method of Example 16:

Prepolymer data (sol):

Intrinsic viscosity: 0.423 [dl/g]

N content: 1.32%

Crosslinking agent content: 0.62 meq/g

Acid content: 0.32 meq/g

Acetate content: 7.8 mol %

Solids content:

30% in the sol state result in

32.6% in the gel state.

21c): 30 g of acetal from Example 1 and 24 g of acidic modifier acetalfrom Example 12, preparation method of Example 15 using 500 g of aceticacid, reaction time 24 hours:

Prepolymer data (sol):

Intrinsic viscosity: 0.331 [dl/g]

N content: 1.18%

Crosslinking agent content: 0.52 meq/g

Acid content: 035 meq/g

Acetate content: 103 mol %

Solids content:

30% in the sol state result in

27.0% in the gel state.

21d): 20 g of acetal from Example 1 and 24 g of acidic modifier acetalfrom Example 12, preparation method of Example 16, reaction time 9hours:

Prepolymer data (sol):

Intrinsic viscosity: 0.390 [dl/g]

N content: 0.994%

Crosslinking agent content: 0.35 meq/g

Acid content: 0.35 meq/g

Acetate content 8.0 mol %

EXAMPLES 22a) AND b)

Products of the reaction of PVA (Mowiol 488, Hoechst) with acetal fromExample 1 and aminobutyraldehyde diethyl acetal, preparation method ofExample 16, isolation by ultrafiltration:

22a): 39 g of acetal from Example 1 and 20 g of ω-aminobutyraldehydediethyl acetal, preparation method of Example 16, reaction time 9 hours:

Prepolymer data (sol):

Intrinsic viscosity: 0.423 [dl/g]

N content: 1.37%

Crosslinking agent content: 0.64 meq/g

Amine content: 0.35 meq/g

Acetate content: 10.0 mol %

Solids content:

30% in the sol state result in

30.6% in the gel state.

22b): 30 g of acetal from Example 1 and 5.2 g of ω-aminobutyraldehydediethyl acetal, preparation method of Example 15, 500 g of added aceticacid, reaction time 24 hours:

Prepolymer data (sol):

Intrinsic viscosity: 0.339 dl/g

N content: 0.89%

Crosslinking agent content: 0.54 meq/g

Amine content: 0.10 meq/g

Acetate content 12.0 mol %

Solids content:

30% in the sol state result in

29.6% in the gel state.

EXAMPLES 23a) AND b)

Products of the reaction of PVA (Mowiol 4-88, Hoechst) with acetal fromExample 1 and crotonaldehyde or butyraldehyde, preparation method ofExample 16, isolation by ultrafiltration.

23a): 30 g of acetal from Example 1 and 19.1 g of butyraldehyde,preparation method of Example 16, reaction time 20 hours at 25° C.:

Prepolymer data (sol):

Intrinsic viscosity: 0.310 dl/g

N content: 0.78%

Crosslinking agent content: 056 meq/g

Acetate content: 2.8 mol %

GPC: M_(w)=22,203, M_(n)=6505, M_(w)/M_(n)=3.41

Solids content:

30% in the sol state result in

32.6% in the gel state.

23b): 30 g of acetal from Example 1 and 18.6 g of crotonaldehyde,preparation method of Example 16, reaction time 20 hours at 25° C.:

Prepolymer data (sol):

Intrinsic viscosity: 0390 dl/g

N content: 0.78%

Crosslinking agent content: 0.56 meq/g

Acetate content: 3.0 mol %

GPC: M_(w)=41,094, M_(n)=15,014, M_(w)/M_(n)=2.73

Solids content:

30% in the sol state result in

30.0% in the gel state.

EXAMPLE 24

Products of the reaction of PVA (Mowiol 488, Hoechst) with acetal fromExample 1 and the pyrrolidone acetal from Example 14, preparation methodof Example 15, isolation by ultrafiltration:

32 g of acetal from Example 1 and 64 g of pyrrolidone acetal fromExample 14, 100 g of added acetic acid

Prepolymer data (sol):

Intrinsic viscosity: 0.340 dl/g

N content 2.72%

Crosslinking agent content: 0.52 meq/g

Acetate content: 6.0 mol %

Solids content:

30% in the sol state result in

29.8% in the gel state.

EXAMPLES 25a) AND b)

Products of the reaction of copolymers of vinyl acetate andvinylpyrrolidone (Luviskol, BASF) with acetal from Example 1, isolationby ultrafiltration using a 1KD ultrafiltration membrane (Millipore).

General preparation method, apparatus as in Example 16

25a): 109.5 g of HCl (37%) are added to 500 g of Luviskol VA 37 HM 50%in ethanol, from BASF. 486 g of water are slowly added over the courseof 4 hour, and the mixture is stirred at 40° C. for 24 hours. The ethylacetate formed and the alcohol are removed in vacuo (15 mbar) in thecourse of 25 hours and replaced by water. The mixture is cooled to roomtemperature, 16.25 g of acetal from Example 1 are added, and the mixtureis stirred at 20° C. for 20 hours.

Isolation by ultrafiltration after neutralization of the reactionsolution to pH 7.0 using NaOH.

425 g of a 13.59% polymer solution (82% of theory) are obtained.

Prepolymer data (sol):

Intrinsic viscosity: 0509 dl/g

N content: 6.22%

Crosslinking agent content: 2.8 mol %

Acetate content: 0.26 meq/g

GPC data: M_(w) 186,102, M_(n) 8497, M_(w)/M_(n) 21.9

Solids content:

(after exposure to 80 mW/cm² for 6 seconds)

30% in the sol state result in

43.1% in the gel state

25b): 405 g of Luviskol VA37E (BASF), 50% in ethanol, are treatedanalogously to Example 25a with 88.7 g of HCl (37%) at 40° C. for 7hours. After the solvent has been removed in vacuo and replaced bywater, 20 g of acetal from Example 1 are added. After 20 hours at roomtemperature, the mixture is neutralized and purified by ultrafiltration(1KD membrane).

Prepolymer data (sol):

N content: 5.45%

Crosslinking agent content: 4.2 mol %

GPC data: M_(w) 38,143, M_(n) 7816, M_(w)/M_(n) 4.88

Solids content:

(after exposure at 80 mW/cm² for 6 seconds)

30% in the sol state result in

34.1% in the gel state

25c): 263 g of Mowilith 30 (Hoechst) are swollen overnight in 500 g ofmethanol and then warmed to 50° C. When the polymer has dissolvedcompletely, 100 g of conc. hydrochloric acid are slowly added at 40° C.,and 530 g of water are subsequently added over the course of 2 hours atsuch a rate that no cloudiness forms. The methanol is removed over afurther 2 hours at 40° C. under a water-pump vacuum. The solution iscooled to 20° C., and 23 g of the acetal from Example 1 are added. Aftera reaction time of 16 hours at room temperature, the solution isadjusted to pH=4 using 5% sodium hydroxide solution. Purification is byultrafiltration through a 1KD Filtron membrane.

Prepolymer data (sol):

Intrinsic viscosity: 0.344 dl/g

N content: 0.79%

Crosslinking agent content: 0.57 meq/g

Acetate content: 20.1 mol %

Cloud point: 61° C.

Solids content:

30% in the sol state result in

32.9% in the gel state

EXAMPLE 26

Production of Contact Lenses via Crosslinking

a) Free-radical photocrosslinking:

0.3% (based on the polymer content) of the photoinitiator Irgacure 295.9is added to a 30% solution of the polymers from Examples 17a to 25c)inclusive. In a transparent polypropylene contact-lens mould, thesolutions are exposed to a 200 W Oriel UV lamp (150 mW/cm²) for 6seconds. The lenses are removed from the mould. They are transparent.

b) Photodimerization:

Products of the reaction of PVA (Mowiol 4-88, Hoechst) with variousphotodimerizing acetals by the general preparation method from Example16, isolation, purification and concentration by ultrafiltration (5KDMillipore membrane):

b1) 15 g of the acetal from Example 7 and 30 g of conc. hydrochloricacid are added to 50 g of PVA (Mowiol 488, Hoechst) dissolved in 250 gof water. The mixture is stirred at 20° C. and, after 24 hours, adjustedto pH 3.6 using 5% sodium hydroxide solution. The solution is subjectedto ultrafiltration through a 5KD Millipore membrane (polymer yield 81%).

Prepolymer data (sol):

Intrinsic viscosity: 0.463 dl/g

N content: 1.11%

Crosslinking agent content: 0.8 meq/g

Acetate content: 1.9 mol %

Crosslinking:

a 30% polymer solution is sensitized by means of 5% of sodium2-phenylquinoxaline4sulfonate and exposed for 5minutes (83 mW/cm³,giving a hydrogel with 6.6% expansion.

b2) 30 g of the acetal from Example 8 and 60 g of conc. hydrochloricacid are added to 100 g of PVA (Mowiol 4-88, Hoechst) dissolved in 500 gof water. The mixture is stirred at 20° C. and, after 24 hours, adjustedto pH 3.6 using 5% sodium hydroxide solution. The solution is subjectedto ultrafiltration through a 5KD Millipore membrane (polymer yield79.5%).

Prepolymer data (sol):

Intrinsic viscosity: 0.367 dl/g

N content: 2.7%

Crosslinking agent content: 0.96 meq/g

Acetate content: 23 mol %

Crosslinking:

a 30% polymer solution is sensitized by means of 5% of sodium2-phenylquinoxaline-4sulfonate and exposed for 5 minutes (83 mW/cm²),giving a hydrogel with 5.3% expansion.

c) Thermal Crosslinking (by Oxidation):

Products of the reaction of PVA (Mowiol 488, Hoechst) with thethiol-containing acetal from Example 13, preparation method of Example15, isolation by ultrafiltration. 33.4 g of the acetal from Example 13,440 g of added acetic acid, no acetal crosslinking agent.

Prepolymer data (sol):

Intrinsic viscosity: 0382 dl/g

Modifier content: 2.3 mol %

Acetate content: 11.0 mol %

GPC: M_(w) 35,250, M_(n) 6934, M_(w)/M_(n) 5.08.

Solids content:

Polymer is not photosensitive, crosslinks thermally.

This example clearly shows that a thiol group is a crosslinkable group.

What is claimed is:
 1. A prepolymer which is a derivative of a polyvinyl alcohol having a mean molecular weight of at least about 2000 which comprises from about 0.5 to about 80%, based on the number of hydroxyl groups in the polyvinyl alcohol, of units of the formula II and units selected from the group consisting of units of formula I and II:

in which R is a bivalent radical of a C₁-C₁₂alkane, R₁ is hydrogen, a C₁-C₆alkyl radical or a cycloalkyl radical, R₂ is hydrogen or a C₁-C₆alkyl radicals R₃ is the

 group if n=0, or the

 bridge if n=1, R₄ is hydrogen or C₁-C₄alkyl, n is zero or 1 and R₁₆ and R₁₇, independently of one another, are hydrogen, C₁-C₈alkyl, aryl or cyclohexyl;

in which R₁ is hydrogen, a C₁-C₆alkyl radical or a cycloalkyl radical, R₅ is a monovalent or bivalent radical of a C₁-C₈alkane or a monovalent or bivalent radical of a C₂-C₈olefin, R₆ is a group of the formula NH—CO—R₇)_(o)(R₈)_(p) or —N(R₉)₂, R₇ is an unsubstituted or substituted monovalent or bivalent radical of a C₁-C₈alkane, R₈ is a heterocyclic group, R₉ is hydrogen or a C₁-C₆alkyl radical, n is zero or 1, and o and p, independently of one another, are zero or 1;

in which R₁₅ is hydrogen or a C₁-C₄alkyl group, in particular CH₃, and p is from zero to
 6. 2. A prepolymer according to claim 1, which comprises units of the formulae I and II.
 3. A prepolymer according to claim 1, which comprises units of the formula III.
 4. A prepolymer according to claim 1, wherein n=0.
 5. A prepolymer according to claim 1, wherein p=0. 